Additional fix for bug #13573

sql/item_func.cc:
  don't return NULL when we got E_DEC_OVERFLOW

sql/item_func.cc

@@ -1124,6 +1124,7 @@ my_decimal *Item_func_div::decimal_op(my_decimal *decimal_value)
 {
   my_decimal value1, *val1;
   my_decimal value2, *val2;
+  int err;
 
   val1= args[0]->val_decimal(&value1);
   if ((null_value= args[0]->null_value))
@@ -1131,17 +1132,15 @@ my_decimal *Item_func_div::decimal_op(my_decimal *decimal_value)
   val2= args[1]->val_decimal(&value2);
   if ((null_value= args[1]->null_value))
     return 0;
-  switch (my_decimal_div(E_DEC_FATAL_ERROR & ~E_DEC_DIV_ZERO, decimal_value,
-                         val1, val2, prec_increment)) {
-  case E_DEC_TRUNCATED:
-  case E_DEC_OK:
-    return decimal_value;
-  case E_DEC_DIV_ZERO:
+  if ((err= my_decimal_div(E_DEC_FATAL_ERROR & ~E_DEC_DIV_ZERO, decimal_value,
+                           val1, val2, prec_increment)) > 3)
+  {
+    if (err == E_DEC_DIV_ZERO)
       signal_divide_by_null();
-  default:
-    null_value= 1;                              // Safety
+    null_value= 1;
     return 0;
   }
+  return decimal_value;
 }